1. Field of the Invention
This invention relates to a magnetic head and more particularly to a magnetic head called MIG (metal in gap) head which is manufactured by depositing a thin magnetic metal film on a magnetic oxide material and by arranging the thin magnetic metal film in the neighborhood of a magnetic gap.
2. Description of the Related Art
A head of the kind called MIG head which is capable of recording or reproducing on or from a magnetic recording medium of high coercive force such as a tape to which a metal is applied or a metal deposited tape has recently come to be employed. In the case of the MIG head, the most part of the core thereof is made of a high permeability material such as ferrite while the fore end part of the magnetic pole near to the gap part of the head is formed with a thin magnetic alloy film of high saturation flux density such as a permalloy, Sendust or amorphous alloy material.
FIGS. 1(A) and 1(B) show in a most simplified form a portion of the MIG head around an electro-magnetic conversion part thereof. A high permeability chip 301 is made of a single crystal ferrite material or the like. A magnetic alloy film 302 is made of an alloy of high saturation flux density such as Sendust or the like. A magnetic gap part 303 is formed by a non-magnetic material. FIG. 1(A) shows the MIG head of the type which has no magnetic alloy film 302 applied to the inside of a groove provided for a winding. FIG. 1(B) shows another type which has the inside of the winding groove coated also with the magnetic alloy film 302. In the case of FIGS. 1(A) and 1(B), a boundary between the high permeability chip 301 and the magnetic alloy film 302 is arranged to be in parallel to a face which slides over the surface of the magnetic recording medium. (Hereinafter this arrangement is referred to as P type.) Meanwhile, the MIG head includes another type which has the above stated boundary arranged to be not in parallel with the magnetic gap part but to have an azimuth angle relative to the latter. (Hereinafter that arrangement is referred to as A type.)
For example, an example of the MIG head of the P type is disclosed in Japanese Patent Application Laid-Open No. SHO 51-140708. An example of the MIG head of the A type is disclosed in Japanese Patent Application Laid-Open No. SHO 60-32107. In the case of the MIG head of the P type, there is a discontinuity in the magnetic property of the head at the boundary between the magnetic alloy film and the high permeability chip which is in parallel to the magnetic gap part. This discontinuity brings about a phenomenon called a contour effect. In other words, there appears a ripple of about 3 to 4 dB or more in a frequency pair output characteristic curve as shown in FIG. 2. This shortcoming has prevented the P type MIG head from being employed for recording or reproducing head. The A type MIG head has been contrived to avoid the above stated phenomenon and has been put to use for VTRs in a manner as disclosed in the above stated Japanese Patent Application Laid-Open No. SHO 60-32107.
The present applicant has previously filed U.S. patent application Ser. No. 900,881 disclosing a magnetic head which obviates the necessity of joining two half cores of an MIG head to each other with varied modes of embodiment thereof. The same applicant also has filed U.S. patent application Ser. No. 917,152 disclosing with varied modes of embodiments a magnetic head characterized by advantageous arrangement of faces on which a magnetic metal film is to be deposited in an MIG head.
Generally, the structural arrangement of the A type MIG head is more complex than that of the P type MIG head and thus has necessitated a greater number of manufacturing processes which results in a higher cost.
Further, in cases where the A type MIG head is to be manufactured to have a wide track width measuring, say, 60 .mu.m, the head necessitates, depending on its structural arrangement and the manufacturing method employed, a process of forming a magnetic alloy film of thickness about 40 .mu.m by some physical depdsiting method such as sputtering. However, a long period of several hours is necessary just for forming the film in such a thickness by sputtering. Moreover, after the formation of the film, accumulated internal stress would cause cracks not only in the film but also in the ferrite base plate thereof. In some extreme case, the base plate might be broken. Therefore, under the severe conditions of manufacturing processes such as a machining process, a glass welding process to be carried out at a high temperature of 500.degree. to 600.degree. C., etc., the head often fails to be finished in a perfect state. The yield rate of the manufacture thus tends to lower.